Very likely this would not constitute unauthorized employment, since it is not employment.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
This is a tricky issue.
First you ask about receiving royalty ... then you say you're not receiving royalty.
I would say that if you are paid into your foreign bank account and that the sales are infrequent ... you're probably OK.
If this is bringing in enough money to pay the rent .. (which, as a photographer myself, I know is difficult) you may have a problem.
Meet with an attorney and your foreign student adviser.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
If you took the pictures while on F-1 status, it could be considered unauthorized employment.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.